Current fluid catalytic cracking unit air rings have their nozzles mounted therein at a 90.degree. angle to the air ring and to the main body of air flow therein as illustrated in FIG. 1 of assignee's U.S. Pat. No. 4,223,243 and in U.S. Pat. No. 2,798,030. Great amounts of nozzle erosion have resulted from this type of nozzle installation, especially when the air flow rates drop to lower than design air flow rates. It is hypothesized that this erosion is caused by pressure differences within the nozzles, wherein as the air ring air flow makes its 90.degree. turn into the nozzle, air flow is directed against the outside portion of the nozzle for the length thereof resulting in a low pressure area formed on the other or inner side of the turn as the high velocity air makes the 90.degree. turn into the nozzle, the low pressure being most pronounced in the upstream portion of the nozzle. This low pressure area is deemed, in the present example, to draw catalyst from the regenerator up into the nozzle and then to circulate within the nozzle, causing erosion of the nozzle internal surface.